build(deps): bump gatsby-transformer-yaml from 2.4.11 to 2.8.0 in /docs

Bumps [gatsby-transformer-yaml](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-yaml) from 2.4.11 to 2.8.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-transformer-yaml/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/gatsby-transformer-yaml@2.8.0/packages/gatsby-transformer-yaml)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docs/package-lock.json

@@ -37,7 +37,7 @@
     "gatsby-source-filesystem": "^2.8.1",
     "gatsby-transformer-remark": "^2.13.1",
     "gatsby-transformer-sharp": "^2.9.0",
-    "gatsby-transformer-yaml": "^2.4.11",
+    "gatsby-transformer-yaml": "^2.8.0",
     "polished": "^4.0.5",
     "prism-react-renderer": "^1.1.1",
     "prop-types": "^15.7.2",